1. Field of the Invention
The invention relates to electrical sliding contacts. A sliding contact is provided between a metallic, e.g. golden sliding track being electrically contacted by a brush, for example a metallic wire, the latter being positioned to slide over the sliding track, if the sliding track and/or the brush are moved relative to each other. Sliding contacts allow for electrical transmission of data and/or energy between the sliding track and the brush, where the brush and the track may be moved relative to each other. For example, the sliding track may be a ring or a ring segment and may be driven to rotate about its center axis. A brush and ring combination is a slip ring assembly.
2. Description of Relevant Art
Sliding contacts are particularly useful in slip ring assemblies. In this case the sliding track is a ring or ring segment like and thus referred to as slip ring. The slip ring may rotate relative to the brush. The brush may be static relative to a given coordinate system. Alternatively the sliding track, i.e. the slip ring may be static and the brush be moved relative to the given coordinate system. The third alternative is that the brush and the slipring move relative to a given coordinate system. Often slip rings have a contact surface made of a precious metal like gold (Au) or silver (Ag) to provide a sliding contact with a low resistance. However, pure Au is supple and thus worn off quickly if contacted in particular by non Au metallic wires as brush.
U.S. Pat. No. 4,398,113 suggests to contact an Au-sliding track with a brush having a higher resistance against abrasion than the Au-sliding track. In an initial run-in period, Au from the sliding track attaches to the brush, yielding a long lasting brush and a reduced friction between the sliding track and the brush.
WO 2013/007458 A2 discloses a slip ring assembly with a sliding track for being contacted by a brush. The sliding track is a double layer sliding track with a first layer having a higher resistance against abrasion than the Au-layer on top of the first layer. The material of the brush is chosen to have a resistance against abrasion between the resistance against abrasion of the first layer and the resistance against abrasion of the Au-layer. Thereby, first the first Au-layer is worn of and subsequently the brush, which is easy to detect. The first layer is harder, i.e. has a higher rigidity than the Au-layer. This enhances the life time of the Au-layer.
WO 2005/038985 relates to an electrical contact element having a contact layer. Said contact layer comprises a film of an amorphous carbide or nitride with the composition Mn+1AXn where n is a positive integer; M one of Scandium, Titanium, Vandum, Chromium, Zirconium, Niobium, Molybdenum, Hafnium or Tantalum; A one of Aluminium, Silicon, Phospor, Sulfur, Gallium, Germanium, Arsenic Cadmium, Indium, Tin, Thallium or Lead and X is Carbon, Nitrogen or both. The layer has amorphous regions of said Mn+1AXn mixed with regions of said material in a nano-crystal state, This layer is supposed to have a low frictional coefficient and is thus wear resistant.
U.S. 2004/0000834 A1 relates to a commutator with commutator sliding members. The sliding members comprise a layer consisting of graphite, metal powders, binder, a solid lubricant and carbon nano tubes or carbon nano fibers. The components are mixed, molded and baked.